First, an almost invisible change: he starts planning for possible negative fates. That is to say, he makes his will and gives it to Utterson. He knows things might go wrong. A second change: he goes ahead with his experimentation anyway. When Utterson sees Jekyll in Part 2, Jekyll looks "deathly sick" and carries himself with a "feverish manner." Both of these are changes in body (and the second a change in mind). In Part 3, Jekyll loses control of his fate (also body and mind, to Hyde); this means he is now at the mercy of others. Finally, though, he becomes responsible: forcing himself into a situation where he'd be punished for his crimes (as Hyde).

Not only did he change mentally but also physically and the changes can be seen due to the fact that his character is becoming much easier to understand and it seems as if though Jekyll acts like a drugee and Mr.Hyde is the drug which gives power to those things he can do when he is not bounded by law